Carbon nanotube, a novel carbon material, was theoretically predicted and experimentally shown to possess unique electronic and mechanical properties and is of great scientific and potential commercial value. Recent studies reveal that the diameter, number of concentric cylinders and helicity of the arrangement of the carbon atoms in the nanotube shell determine whether the nanotube has metallic, semiconducting or insulating properties. Hence a wide range of materials properties may be "tuned in" by changing the structural properties of these nanotubes. The stiffness and high strength of these carbon nanotubes make them ideal probes in scanning probe microscopy, and efficient field-emitters, as recently shown by Smalley's group. Additionally the inner hollow cavity of the nanotubes may serve as nanometer scale test tubes in which to carry out interesting experiments with submicroscopic quantities of reagents. Nanotubes filled with metallic or semiconducting particles might serve as the constituents of novel materials with useful magnetic, electrical or electronic properties leading to new devices.
The conventional synthesis methods for carbon nanotube include carbon arc discharge (S. lijima, Nature, 354, 56, 1991) and catalytic pyrolysis of hydrocarbon (M. Endo, K. Takeuchi, S. Igarashi, K. Kobori, M. Shiraishi, H. W. Kroto, J. Phys. Chem. Solids, 54, 1841, 1993), which generate nanotubes often containing traces of the catalyst particles used to generate them and possessing highly variable dimensions. Synthesis of aligned nanotube by pyrolysis of hydrocarbon with a patterned cobalt catalyst on silica substrate was recently reported by M. Terrones et al, Nature, 388, 52, 1997 and with iron nanoparticles in mesoporous silica by W. Z. Li et al, Science, 274, 1701, 1996. The successful production of carbon nanotubes in an alumina template by pyrolysis of propylene has been disclosed by T. Kyotani, L. Tsai, A. Tomita, Chem. Mater., 8, 2190, 1996.
The encapsulation of foreign materials in the carbon nanotubes has been disclosed by P. M. Ajayan and S. lijima (U.S. Pat. No. 5,457,343). Ni, Fe, Co, rare earth metals and their carbides were found to be encapsulated in the nanotubes during synthesis of them in carbon arc discharge by Y. Saito et al, J. Phys. Chem. Solids, 54, 1849, 1993, and also by C. Guerret-Piecout et al, Nature, 372, 761, 1994. The metals with a low melting point, such as lead, zinc, selenium, and molten metal salt, AgNO.sub.3 were filled through capillarity into the carbon nanotubes, reported by P. M. Ajayan et al, Nature, 362, 522, 1993, E. Dujardin et al, Science 265, 1850, 1994 and by D. Ugarte et al, Science, 274, 1897, 1996.